icuSources/common/unicode/bytestream.h

   1 // © 2016 and later: Unicode, Inc. and others.
   2 // License & terms of use: http://www.unicode.org/copyright.html
   3 // Copyright (C) 2009-2012, International Business Machines
   4 // Corporation and others. All Rights Reserved.
   5 //
   6 // Copyright 2007 Google Inc. All Rights Reserved.
   7 // Author: sanjay@google.com (Sanjay Ghemawat)
   8 //
   9 // Abstract interface that consumes a sequence of bytes (ByteSink).
  10 //
  11 // Used so that we can write a single piece of code that can operate
  12 // on a variety of output string types.
  13 //
  14 // Various implementations of this interface are provided:
  15 //   ByteSink:
  16 //      CheckedArrayByteSink    Write to a flat array, with bounds checking
  17 //      StringByteSink          Write to an STL string
  18
  19 // This code is a contribution of Google code, and the style used here is
  20 // a compromise between the original Google code and the ICU coding guidelines.
  21 // For example, data types are ICU-ified (size_t,int->int32_t),
  22 // and API comments doxygen-ified, but function names and behavior are
  23 // as in the original, if possible.
  24 // Assertion-style error handling, not available in ICU, was changed to
  25 // parameter "pinning" similar to UnicodeString.
  26 //
  27 // In addition, this is only a partial port of the original Google code,
  28 // limited to what was needed so far. The (nearly) complete original code
  29 // is in the ICU svn repository at icuhtml/trunk/design/strings/contrib
  30 // (see ICU ticket 6765, r25517).
  31
  32 #ifndef __BYTESTREAM_H__
  33 #define __BYTESTREAM_H__
  34
  35 /**
  36  * \file
  37  * \brief C++ API: Interface for writing bytes, and implementation classes.
  38  */
  39
  40 #include "unicode/utypes.h"
  41 #include "unicode/uobject.h"
  42 #include "unicode/std_string.h"
  43
  44 #if U_SHOW_CPLUSPLUS_API
  45 U_NAMESPACE_BEGIN
  46
  47 /**
  48  * A ByteSink can be filled with bytes.
  49  * @stable ICU 4.2
  50  */
  51 class U_COMMON_API ByteSink : public UMemory {
  52 public:
  53   /**
  54    * Default constructor.
  55    * @stable ICU 4.2
  56    */
  57   ByteSink() { }
  58   /**
  59    * Virtual destructor.
  60    * @stable ICU 4.2
  61    */
  62   virtual ~ByteSink();
  63
  64   /**
  65    * Append "bytes[0,n-1]" to this.
  66    * @param bytes the pointer to the bytes
  67    * @param n the number of bytes; must be non-negative
  68    * @stable ICU 4.2
  69    */
  70   virtual void Append(const char* bytes, int32_t n) = 0;
  71
  72   /**
  73    * Returns a writable buffer for appending and writes the buffer's capacity to
  74    * *result_capacity. Guarantees *result_capacity>=min_capacity.
  75    * May return a pointer to the caller-owned scratch buffer which must have
  76    * scratch_capacity>=min_capacity.
  77    * The returned buffer is only valid until the next operation
  78    * on this ByteSink.
  79    *
  80    * After writing at most *result_capacity bytes, call Append() with the
  81    * pointer returned from this function and the number of bytes written.
  82    * Many Append() implementations will avoid copying bytes if this function
  83    * returned an internal buffer.
  84    *
  85    * Partial usage example:
  86    *  int32_t capacity;
  87    *  char* buffer = sink->GetAppendBuffer(..., &capacity);
  88    *  ... Write n bytes into buffer, with n <= capacity.
  89    *  sink->Append(buffer, n);
  90    * In many implementations, that call to Append will avoid copying bytes.
  91    *
  92    * If the ByteSink allocates or reallocates an internal buffer, it should use
  93    * the desired_capacity_hint if appropriate.
  94    * If a caller cannot provide a reasonable guess at the desired capacity,
  95    * it should pass desired_capacity_hint=0.
  96    *
  97    * If a non-scratch buffer is returned, the caller may only pass
  98    * a prefix to it to Append().
  99    * That is, it is not correct to pass an interior pointer to Append().
 100    *
 101    * The default implementation always returns the scratch buffer.
 102    *
 103    * @param min_capacity required minimum capacity of the returned buffer;
 104    *                     must be non-negative
 105    * @param desired_capacity_hint desired capacity of the returned buffer;
 106    *                              must be non-negative
 107    * @param scratch default caller-owned buffer
 108    * @param scratch_capacity capacity of the scratch buffer
 109    * @param result_capacity pointer to an integer which will be set to the
 110    *                        capacity of the returned buffer
 111    * @return a buffer with *result_capacity>=min_capacity
 112    * @stable ICU 4.2
 113    */
 114   virtual char* GetAppendBuffer(int32_t min_capacity,
 115                                 int32_t desired_capacity_hint,
 116                                 char* scratch, int32_t scratch_capacity,
 117                                 int32_t* result_capacity);
 118
 119   /**
 120    * Flush internal buffers.
 121    * Some byte sinks use internal buffers or provide buffering
 122    * and require calling Flush() at the end of the stream.
 123    * The ByteSink should be ready for further Append() calls after Flush().
 124    * The default implementation of Flush() does nothing.
 125    * @stable ICU 4.2
 126    */
 127   virtual void Flush();
 128
 129 private:
 130   ByteSink(const ByteSink &) = delete;
 131   ByteSink &operator=(const ByteSink &) = delete;
 132 };
 133
 134 // -------------------------------------------------------------
 135 // Some standard implementations
 136
 137 /**
 138  * Implementation of ByteSink that writes to a flat byte array,
 139  * with bounds-checking:
 140  * This sink will not write more than capacity bytes to outbuf.
 141  * If more than capacity bytes are Append()ed, then excess bytes are ignored,
 142  * and Overflowed() will return true.
 143  * Overflow does not cause a runtime error.
 144  * @stable ICU 4.2
 145  */
 146 class U_COMMON_API CheckedArrayByteSink : public ByteSink {
 147 public:
 148   /**
 149    * Constructs a ByteSink that will write to outbuf[0..capacity-1].
 150    * @param outbuf buffer to write to
 151    * @param capacity size of the buffer
 152    * @stable ICU 4.2
 153    */
 154   CheckedArrayByteSink(char* outbuf, int32_t capacity);
 155   /**
 156    * Destructor.
 157    * @stable ICU 4.2
 158    */
 159   virtual ~CheckedArrayByteSink();
 160   /**
 161    * Returns the sink to its original state, without modifying the buffer.
 162    * Useful for reusing both the buffer and the sink for multiple streams.
 163    * Resets the state to NumberOfBytesWritten()=NumberOfBytesAppended()=0
 164    * and Overflowed()=FALSE.
 165    * @return *this
 166    * @stable ICU 4.6
 167    */
 168   virtual CheckedArrayByteSink& Reset();
 169   /**
 170    * Append "bytes[0,n-1]" to this.
 171    * @param bytes the pointer to the bytes
 172    * @param n the number of bytes; must be non-negative
 173    * @stable ICU 4.2
 174    */
 175   virtual void Append(const char* bytes, int32_t n);
 176   /**
 177    * Returns a writable buffer for appending and writes the buffer's capacity to
 178    * *result_capacity. For details see the base class documentation.
 179    * @param min_capacity required minimum capacity of the returned buffer;
 180    *                     must be non-negative
 181    * @param desired_capacity_hint desired capacity of the returned buffer;
 182    *                              must be non-negative
 183    * @param scratch default caller-owned buffer
 184    * @param scratch_capacity capacity of the scratch buffer
 185    * @param result_capacity pointer to an integer which will be set to the
 186    *                        capacity of the returned buffer
 187    * @return a buffer with *result_capacity>=min_capacity
 188    * @stable ICU 4.2
 189    */
 190   virtual char* GetAppendBuffer(int32_t min_capacity,
 191                                 int32_t desired_capacity_hint,
 192                                 char* scratch, int32_t scratch_capacity,
 193                                 int32_t* result_capacity);
 194   /**
 195    * Returns the number of bytes actually written to the sink.
 196    * @return number of bytes written to the buffer
 197    * @stable ICU 4.2
 198    */
 199   int32_t NumberOfBytesWritten() const { return size_; }
 200   /**
 201    * Returns true if any bytes were discarded, i.e., if there was an
 202    * attempt to write more than 'capacity' bytes.
 203    * @return TRUE if more than 'capacity' bytes were Append()ed
 204    * @stable ICU 4.2
 205    */
 206   UBool Overflowed() const { return overflowed_; }
 207   /**
 208    * Returns the number of bytes appended to the sink.
 209    * If Overflowed() then NumberOfBytesAppended()>NumberOfBytesWritten()
 210    * else they return the same number.
 211    * @return number of bytes written to the buffer
 212    * @stable ICU 4.6
 213    */
 214   int32_t NumberOfBytesAppended() const { return appended_; }
 215 private:
 216   char* outbuf_;
 217   const int32_t capacity_;
 218   int32_t size_;
 219   int32_t appended_;
 220   UBool overflowed_;
 221
 222   CheckedArrayByteSink() = delete;
 223   CheckedArrayByteSink(const CheckedArrayByteSink &) = delete;
 224   CheckedArrayByteSink &operator=(const CheckedArrayByteSink &) = delete;
 225 };
 226
 227 /**
 228  * Implementation of ByteSink that writes to a "string".
 229  * The StringClass is usually instantiated with a std::string.
 230  * @stable ICU 4.2
 231  */
 232 template<typename StringClass>
 233 class StringByteSink : public ByteSink {
 234  public:
 235   /**
 236    * Constructs a ByteSink that will append bytes to the dest string.
 237    * @param dest pointer to string object to append to
 238    * @stable ICU 4.2
 239    */
 240   StringByteSink(StringClass* dest) : dest_(dest) { }
 241   /**
 242    * Constructs a ByteSink that reserves append capacity and will append bytes to the dest string.
 243    *
 244    * @param dest pointer to string object to append to
 245    * @param initialAppendCapacity capacity beyond dest->length() to be reserve()d
 246    * @stable ICU 60
 247    */
 248   StringByteSink(StringClass* dest, int32_t initialAppendCapacity) : dest_(dest) {
 249     if (initialAppendCapacity > 0 &&
 250         (uint32_t)initialAppendCapacity > (dest->capacity() - dest->length())) {
 251       dest->reserve(dest->length() + initialAppendCapacity);
 252     }
 253   }
 254   /**
 255    * Append "bytes[0,n-1]" to this.
 256    * @param data the pointer to the bytes
 257    * @param n the number of bytes; must be non-negative
 258    * @stable ICU 4.2
 259    */
 260   virtual void Append(const char* data, int32_t n) { dest_->append(data, n); }
 261  private:
 262   StringClass* dest_;
 263
 264   StringByteSink() = delete;
 265   StringByteSink(const StringByteSink &) = delete;
 266   StringByteSink &operator=(const StringByteSink &) = delete;
 267 };
 268
 269 U_NAMESPACE_END
 270 #endif // U_SHOW_CPLUSPLUS_API
 271
 272 #endif  // __BYTESTREAM_H__